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Argument starter: Power/MPG with Leer cap on 4 cyl. double cab PreRunner

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Old 06-14-2012, 05:09 PM   #1
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Power/MPG change with Leer cap on 4 cyl. double cab PreRunner

Got a 2012 2WD double cab prerunner with the 2.7 I4/auto since it matches what we actually do with a truck (nearly no towing, a bit of light hauling and a lot of on-road driving). So far I'm loving it - enough power for anything I really do and certainly better mileage than my (t)rusty F-150 that it's replacing. And it looks good.

In a high headwind (20+mph) at freeway speeds (70 - 75mph), the engine is on the edge of what it will reasonably handle - putting it on cruise control pretty much locks it into a downshift, though you can manually drive it so that it stays in 4th and maintains speed. Gas mileage is in the 18-19 mpg range under these conditions.

What will happen if I put a cap (I'm looking at the Leer XQ100) on it? A slight reduction of mileage would be okay, but if I can't maintain freeway speed it won't be a good day. Flat bed covers aren't really an option since dry storage volume is needed.

Opinions are all over the place on this...anyone have experiences to share?
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Old 06-20-2012, 02:59 PM   #2
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What you are looking at for mileage changes are weight, and aerodynamics. Most likely, and this is not a rule, the loss of mileage from weight will most likely be regained by the increase in aerodynamics. A lot depends on the shape of the cap, and the weight of it obviously. I doubt you will see much of a difference, if any at all.

Overall, I would say if you do mostly highway driving, you won't notice a change, but if you do mostly city driving, you might have a minute loss of .25 mpg. Think of it this way, you are adding the weight of an average male to your truck. Same as adding an additional passenger. Have you ever noticed a change in your mileage by having an extra person in the vehicle? Doubtful.
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Old 06-21-2012, 07:04 AM   #3
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It is aerodynamically suicide.
What you will have after installing a cap, is a big flat wall on the back of your truck. The bigger the flat wall, the more air you will drag along behind you. Ideally, you would want a cap that slopes down to flush with the top of the tailgate. This would actually improve efficiency.
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Old 06-21-2012, 07:17 AM   #4
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Quote:
Originally Posted by knucklehead View Post
It is aerodynamically suicide.
What you will have after installing a cap, is a big flat wall on the back of your truck. The bigger the flat wall, the more air you will drag along behind you. Ideally, you would want a cap that slopes down to flush with the top of the tailgate. This would actually improve efficiency.
The Leer 100Xq DOES slope on the back... It's not aerodynamically perfect, but it certainly won't make anything any worse.

Honestly, you won't notice much of a difference at highway speed in either MPG or power loss (maybe on long, steep hills the extra weight would be noticable but they're really not THAT heavy). You might notice the truck being a little more sluggish around town due to the extra weight though.
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Old 06-21-2012, 08:05 AM   #5
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Quote:
Originally Posted by Pugga View Post
The Leer 100Xq DOES slope on the back... It's not aerodynamically perfect, but it certainly won't make anything any worse.

Honestly, you won't notice much of a difference at highway speed in either MPG or power loss (maybe on long, steep hills the extra weight would be noticable but they're really not THAT heavy). You might notice the truck being a little more sluggish around town due to the extra weight though.
leer 100xq, notice horizontal roof, vertical back:




aerodynamic sloping:

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Old 06-21-2012, 08:08 AM   #6
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Quote:
Originally Posted by knucklehead View Post
leer 100xq, notice horizontal roof, vertical back:




aerodynamic sloping:

Like I said, it's not aerodynamically perfect, but it won't make a difference over stock... It's sloped enough so it won't create a suction like you were talking about. The gentle curve of the XQ is enough to help airflow. To get suction like you were referring to, you need a true vertical back and sharp corners like a tractor trailer bulk hauler or box truck.
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Old 06-21-2012, 08:27 AM   #7
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Quote:
Originally Posted by Pugga View Post
Like I said, it's not aerodynamically perfect, but it won't make a difference over stock... It's sloped enough so it won't create a suction like you were talking about. The gentle curve of the XQ is enough to help airflow. To get suction like you were referring to, you need a true vertical back and sharp corners like a tractor trailer bulk hauler or box truck.
When open, it is somewhat aerodynamic, because it is open. Fluids dont give a rat's ass if the corners are sharp or round, and that very very minor slope of the back window will not amout to anything at all. Try it in a wind tunnel and you will see just how bad that actually is.

The curves on that thing are cosmetic.
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Old 06-21-2012, 08:32 AM   #8
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Quote:
Originally Posted by knucklehead View Post
When open, it is somewhat aerodynamic, because it is open. Fluids dont give a rat's ass if the corners are sharp or round, and that very very minor slope of the back window will not amout to anything at all. Try it in a wind tunnel and you will see just how bad that actually is.

The curves on that thing are cosmetic.
Curves vs. straight cuts make a very big difference when it comes to aerodynamics...

Once again, I said it's not aerodynamically perfect but the base, unmodified pickup is far from perfect either. The addition of the shell won't make it any worse and certainly isn't 'aerodynamic suicide' as you so nicely put it.
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Old 06-21-2012, 06:10 PM   #10
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Another vote for "you won't notice a difference".

Mike
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Old 06-21-2012, 06:19 PM   #11
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Slight decrease with a topper. Less aerodynamic however those who say not noticeable/barely noticeable are also correct. make up the difference with some exhaust mods, i.e., header, cat back, 2nd air filter delete. All of which will give you very little gain, but, will help haul a little extra weight up a hill and on the highway. . . my .02
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Old 06-21-2012, 06:38 PM   #13
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Cover options

Jeff makes a fair point. Here is a link to a discussion regarding the benefit of a tonneau. Post #12 has a chart with various cover options and benefits on fuel economy.

http://www.cleanmpg.com/forums/showt...hlight=tonneau
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Old 06-25-2012, 06:04 AM   #14
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Quote:
Originally Posted by hookedontronics View Post
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Dropping the tailgate does absolutely nothing to improve MPG. It has been disproved several times. Actually most studies have shown that lowering the tailgate has actually increased drag, and LOWERED the MPG of the trucks. While there are many ideas behind the different toppers and such, the real question is what will the truck be used for, how much cargo will be carried, and personal preference of the owner. While I agree that the sloped topper is better for MPG, I think it looks ugly as all hell! I would never put that on my truck. Again that is personal preference though. Also the sloped topper reduces the cubic feet of storage space on the inside. If the OP were wanting to carry several large boxes on a regular basis, then the sloped design would not look well. If all the OP was concerned with was fuel efficiency, then a sloped topper or a tonneau cover would be good.
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Old 06-25-2012, 09:57 AM   #15
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Some further discussion worth reviewing - http://www.tacomaworld.com/forum/2nd...xperiment.html

Yes, unless the slope is designed into the vehicle, it does look out of place to me. But I can appreciate the experimentation and a pursuit to optimize fuel economy. Pragmatism and practicality of design is essential to the everyday needs of the owner/operator. That's why they have box trucks and bulldozers: practical for the need/application.

Check out the imbedded links in the thread link above. Lots more reading but it helps to shape theory.

Good luck!
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Old 06-25-2012, 08:41 PM   #16
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Aerodynamic suicide?

Here's a study from California State University. http://csus-dspace.calstate.edu/xmlu...pdf?sequence=1
Go directly to the appendix for the results. Drag coefficient is reduced by addition of a "traditional canopy" and is lower than that of a Tonneau cover. Yes, it is all based on modeling.
I saw no change after the canopy was added.
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Old 06-26-2012, 01:59 PM   #17
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I was thinking, what if you installed a camper shell then added an air deflector such as the 98ish 4-runner had?

http://ecomodder.com/forum/87489-post3.html
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Old 07-01-2012, 01:30 PM   #18
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Thanks everyone - I've ordered it and we'll see about the power (the tests will be thoroughly subjective and ad-hoc, and that assumes I can find a reasonably calm day out here in the prairie). Read the Cal State study and am amazed that nobody's really gone through this thoroughly with anything but a student's simulation project (no funding = no study, but still...).

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Old 07-02-2012, 08:49 PM   #19
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Results are in: Pugga is right. No change in engine's ability to hold speed on the freeway (test method is to take a particularly flat stretch of interstate and keep bumping the cruise control up until the transmission starts to downshift - 82mph indicated [80 actual] in both cases). Slightly more sluggish as if there were another person aboard*.

*Sadly, not BamaToy's sig-other-person.
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Old 05-05-2013, 08:36 PM   #20
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Thanks for doing the leg work, getting one soon and was wondering the same thing. Got the I4 DCSB for exact same reasons you did. It's all I need. Wouldn't be worth it to me if the MPG drop was severe as that was a reason I got it as well. No reservations now, looking forward to getting it.
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